Help with finding plastic window part - W116 300SD

[djburt]

Hey all,

I'm fixing my driver's window in my '80 300SD, and can't find this 116 chassis part. It's different than the 126 chassis I've found at the local yard.

I'm not sure what to call it, but it's a plastic piece that fits between the metal bracket (attached to the regulator's arm) and the metal rod that the bracket rolls up and down. It keeps the window from going slanted when the window goes up or down. As you can see, it's broken, so I was having to hold my window while rolling up so it didn't get off track.

Any ideas what this is called and where I can find it? Thanks!